Filtering system for pyrographic recorders

ABSTRACT

A filtering system for removing waste products released during the operation of drum-type pyrographic recorders, such as electroresistive recorders, comprises a filter cartridge which is sealed in a housing between a drum length funnel and the inlet side of a blower. The face of the funnel is in close proximity to the surface of the drum and is apertured so that a partial vacuum is maintained in the immediate area of the drum and along substantially its entire length, while localized separation of the recording medium from the drum is effectively precluded. The partial vacuum causes the waste product laden air to be drawn through the filter cartridge where the solid contaminants are trapped in a first stage and the gaseous contaminants are neutralized in a second stage.

United States Patent [191 Kramell FILTERING SYSTEM FOR PYROGRAPHICRECORDERS Inventor: Hans Peter Kramell, Perry, N.Y.

Assignee: Xerox Corporation, Stamford,

Conn.

Filed: Mar. 19, 1973 Appl. No.: 342,571

US. Cl 346/74 S, 178/94 Int. Cl. H041 15/24, BOld 46/12 Field of Search178/94; 346/74 S, 74 SB, 346/74 SC, 76 R, 76 L; 15/312 R, 312 A; 19/109;55/315, 316, 521; 51/273 References Cited UNITED STATES PATENTS3,697,691 10/1972 vonl-lippel 178/94 Primary Examiner-Thomas A. Robinson[57] ABSTRACT A filtering system for removing waste products releasedduring the operation of drum-type pyrographic recorders, such aselectroresistive recorders, comprises a filter cartridge which is sealedin a housing between a drum length funnel and the inlet side of ablower. The face of the funnel is in close proximity to the surface ofthe drum and is apertured so that a partial vacuum is maintained in theimmediate area of the drum and along substantially its entire length,while localized separation of the recording medium from the drum iseffectively precluded. The partial vacuum causes the waste product ladenair to be drawn through the filter cartridge where the solidcontaminants are trapped in a first stage and the gaseous contaminantsare neutralized in a second stage.

8 Claims, 2 Drawing Figures FILTERING SYSTEM FOR PYROGRAPHIC RECORDERSBACKGROUND OF THE INVENTION This invention relates, generally, tofilters for suppressing the waste products released during pyrographicrecording and, more particularly, to filters for drum-typeelectroresistive recording equipment.

As is known, one of the more widely utilized species of pyrographicrecording is an electroresistive process in which an image is formed byrelying on the current flow between a stylus and a conductive layer of arecording medium to burn away localized areas of an overcoating on therecording medium, thereby exposing a contrasting underlayer in an imageconfiguration. As a general rule, this. process is carried out with relative motion between the stylus and the recording medium so that thestylus traverses the recording medium in accordance with a predeterminedscanning pattern. For example, the electroresistive printing process hasbeen used for several years with substantial success in what is known asthe Xerox 400 Telecopier facsimile transceiver, which is manufacturedand sold by Xerox Corporation. In that unit, the electroresistiverecording paper is wrapped around a rotating drum and the stylus ismounted on a carriage which travels axially of the drum, with the resultthat there is a substantially helical scanning pattern. Hence, almostany desired image may be formed simply by controlling the voltageapplied to the stylus as a function of time, or in other words, as afunction of the position of the stylus relative to the recording medium.Indeed, the art of electroresistive recording has progressed to thepoint that shading of the image can be achieved by additionallycontrolling the magnitude of the voltage applied to the stylus. For thatreason, the aforementioned 400 Telecopier transceiver is generallyrecognized as having a so-called gray scale capability.

Unfortunately, electroresistive recording is accompanied-by the releaseof waste products, including aromatic gases, visible smoke, andparticulate matter. The aromatics are responsible for objectionableodors, while the smoke and the particulate matter cause a residue to bedeposited on the equipment. Analysis of a typical electroresistiverecording process has led to a tentative conclusion that the majorgaseous components evolving are carbon monoxide; ethane; l, and 2-butenes; and n-butylmethacrylate, with the methacrylate being thestrongest and most objectionable of the aromatics. The particulatematter, on the other hand, is believed to principally be small,light-weight ashes.

Others have previously proposed filters for suppressing such wasteproducts. For example, US. Pat. No. 3,697,691, which issued on Oct. 10,1972, purports to describe a' filter for removing carbon particles andgas efflux as an image is electroresistively formed by a drum-typefacsimile machine. However, the prior attempts to solve the problem havenot fully been satisfactory for a number of reasons, including therelative complexity of the filtering equipment that has been suggested,the relatively short life span of the filtering elements used in thatequipment, the high pressure drop which occurs across such filteringelements, and the failure to make full allowance for the turbulentenvironment in which the filtering is taking place.

SUMMARY OF THE INVENTION Thus, the primary aim of the present inventionis to provide a relatively economical and efficient filtering system forsuppressing, if not completely eliminating. the waste products that arereleased during the operation of drum-type pyrographic recorders,including electroresistive recording equipment.

In keeping with that goal, a general object of this invention is toprovide a filtering system which is especially well suited for use withsuch recorders, as measured by the ability of the system to removegaseous and solid contaminants from the area immediately adjacent thedrum and by the input energy required by the system to effect thefiltering action.

More particularly, one of the important objects of the subject inventionis to provide a filtering system which is particularly adept at removingwaste products from the area immediately adjacent the drum of such arecorder, despite the turbulence of the air flow in that area. Anotherof the important objects is to provide a filtering system which not onlysupplies the desired filtering action, but which also aids in counteringthe centrifugal forces which act on the recording medium in such arecorder and which, if uncountered, would upset the recording process byseparating the recording medium from the drum. A more detailed relatedobject is to provide a filtering system with a special configurationwhich not only improves the filtering action that is obtained, but whichalso aids in retaining the recording medium against the drum, therebyyielding a highly beneficial synergistic effect.

A further object of the present invention is to provide a filteringsystem which, in addition to having the aforementioned characteristics,is relatively simple and economical to manufacture and service. Arelated object is to provide a filtering system of the foregoing typewhich has relatively few moving parts and relatively long livedfiltering elements and, therefore, relatively minimal maintenancerequirements.

Still another object of the present invention is to provide a filteringsystem of the foregoing type which may be stored for extended periods oftime without appreciable loss of efficiency.

Consistently with the above stated objects, the filtering system heredisclosed comprises a filtering cartridge which is sealed between anelongated funnel and the inlet side of a suitable air moving device,such as a centrifugal blower. To remove the waste products which arereleased during the operation of a drum-type pyrographic recorder and toaid in countering the centrifugal forces acting on the recording medium,the funnel is aligned in operation with the axis of rotation of the drumand its face, which has an aperture extending substantially the entirelength of the drum, is in close proximity to the surface of the drum,with the aperture a few degrees in advance of the line of travel of thestylus along the drum. The blower, of course, creates a partial vacuumin the immediate area of the drum and along substantially the entirelength thereof so that most of the waste products are ultimately drawnthrough the filtering cartridge, either immediately after being releasedor at some later time, depending upon the unpredictable interactionbetween the waste products and the turbulent air flow in the area of thedrum. The filtering cartridge is a two stage filter; with a first stagecomprising a porous packing to trap airborne particulate matter, such asashes, and the second stage having an activated carbon medium toneutralize gaseous contaminants. Baffles are included in the secondstage to force the air flow through the activated carbon even if thecarbon has settled during storage or other prolonged periods ofinactivity of the filtering cartridge.

BRIEF DESCRIPTION OF THE DRAWINGS Further objects and advantages of thisinvention will become apparent upon reading the following detaileddescription in conjunction with the attached drawings, in which:

FIG. 1 is a simplified, fragmentary perspective view of a portion of apyrographic recorder embodying a filtering system constructed inaccordance with the present invention; and

FIG. 2 is a simplified sectional view taken along the line 22 in FIG. 1.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT While the inventionis described in some detail hereinafter with reference to an illustratedembodiment, it is to be understood that there is no intent to limit itto that embodiment. On the contrary, the intent is to cover allalternatives, modifications and equivalents falling within the spiritand scope of the invention as defined by the appended claims.

Turning now to the drawings, it will be seen that a drum-typepyrographic recorder 11, including a filtering system 12 embodying thepresent invention, has

been diagrammatically depicted. In keeping with a more or lessconventional configuration for pyrographic recorders, the recorder 11comprises a rotatable drum 13 and a stylus 14. Typically in operation ofsuch a recorder, a suitable recording medium (not shown) is wrappedaround the drum 13 which, in turn, is rotated about its longitudinalaxis at a predetermined rate as the stylus 14 is moved lengthwise of thedrum 13 along a line substantially parallel to its axis of rotation. Asa result, a substantially helical scanning pattern is generated with theresult that the stylus 14 can be readily controlled to burn awaylocalized areas of an overcoating on the recording medium, therebyexposing a contrasting underlying layer thereof in an imageconfiguration.

For a more'detailed understanding of the construction and operation ofan exemplary pyrographic recorder with which the filtering system 12 canbe advantageously utilized reference may be had to the electroresistiverecorders comprised by the aforementioned, commercially available Xerox400 Telecopier facsimile transceivers and the published literaturepertaining thereto. Accordingly, attention is here focused primarily onthe filtering system 12.

As shown, the filtering system 12 includes a filtering cartridge 15which is sealed by a pair of gaskets l6 and 17 in a housing 18 between afunnel 19 and the inlet side of a suitable air moving device, such as acentrifugal blower 21. The face 22 of the funnel 19 is apertured as at23 and the outlet or discharge side of the blower 21 is open to theatmosphere. Thus, the blower 21 creates a partial vacuum, therebycausing air to be drawn into the aperture 23 and through the cartridge15 prior to being discharged to the atmosphere. As will be appreciated,the sealing gaskets 16 and 17 mechanically stabilize the cartridge 15and prevent any appreciable leakage of air through the spaces betweenthe cartridge 15 and the housing 18.

In accordance with an important feature of this invention, the filteringsystem 12 serves a dual function or in other words, has a synergisticeffect. That is, it not only removes the waste products that arereleased as an image is formed on the recording medium, but it alsoprecludes any significant localized separation of the recording mediumfrom the drum 13. In the Xerox 400 Telecopier transceiver, for example,there are four wipers (not shown) which are spaced at substantiallyequal angular increments about the periphery of the drum to cooperatewith a gripper bar 24 in retaining the recording medium in contact withthe drum despite the centrifugal forces which tend to cause a separationto occur. As here shown, however, the filtering system 12 permits one ofthe wipers to be eliminated while still retaining its function.

More particularly, to carry out the above noted functions, the funnel 19is elongated and is mounted (by means not shown) so that its face 22 ismaintained in close proximity to the surface of the drum 13; forexample, within 0.05 inches or so thereof. Because of the relativelynarrow gap between the surface of the drum 13 and the face 22 of thefunnel 19, together with the elongated configuration of the funnel,local separation of the recording medium from the drum is effectivelyprecluded. Moreover, advantage may be taken of the elongatedconfiguration of the funnel 19 to optimize the filtering action. To thatend, the aperture 23 is selected to have a length, as measured parallelto the axis of rotation of the drum 13, substantially equal to thelength of the drum 13 so that a partial vacuum is constantly maintainedin the immediate area of the drum along substantially the entire length.Preferably, the aperture 23 is just slightly in advance of the line oftravel of the stylus 14, as measured in the direction of rotation of thedrum. Nevertheless, some of the waste products that are released as animage is formed may, at least initially, be directed away from theaperture 23 as a result of the turbulent air flow which inherentlyoccurs in the immediate area of the drum. Accordingly, it will beunderstood that one of the important characteristics of the filteringsystem 12 is that the filtering action is substantially independent ofthe position of the stylus 14, with the result that waste products maybe captured, either as they are released or at some time later. Ofcourse, transverse stiffening ribs 20 may be spaced at intervals alongthe face 22 of the funnel 19 without materially impairing the filteringaction. The stiffening ribs 20 mechanically strengthen the funnel 19 andalso enhance its wiper action. As illustrated, the filtering cartridge15 has an upstream chamber 25 filled with a porous packing 25a, such asa 6 ounce density, non-woven fiber, for trapping the solid contaminantscarried by the waste product laden air that is drawn therethrough and adownstream chamber 26 filled with an activated carbon medium 26a, suchas the Type 582 activated carbon manufactured and sold by Barnaby &Cheney, Inc., for neutralizing the gaseous contaminants. A relativelylow pressure drop occurs across the filtering section 15 inasmuch as itis substantially coextensive with the aperture 23 and provides agenerally straight through air flow path. Accordingly, the partialvacuum existing at the inlet side of the blower 21, which may be considaered to be the inputlenergy to the filtering system (of coursethatdefinition of the input energy normalizes is made for preventing anyappreciable depletion of theinitial charge. Forexample, the frontandrear of thefchamber 26 may suitably be covered with respectivescreens 27 and 28 with a mesh size selected to precludeleakage oftheactivated carbon medium. Nevertheless, some settling of-the activatedcarbon inherently takes place, especially during prolonged periods ofinactivity or storage of the cartridge 15. Consequently, in keeping withone or more of the detailed aspects of this invention, baffles 31 areincluded in the chamber 26 to force the air passing therethrough toflowthrough the activated carbon even if settling has taken place. Thecritical area of the compartment 26 is, of course, the upper portionthereof since that is where a free space might be found. However, tosimplify the tooling used in the manufacture of the chamber 26 and toavoid any definite upper side-lower side pre-orientation of thecartridge 15, the chamber26 is preferably symmetrical and, therefore,has baffles 31 extending inwardly from both its upper and lower faces.

Thelife span of the non-woven and activated carbon filtering elementsdepends in significant part on their depth. In theinterest ofcompleteness, therefore, it is perhaps worth mentioning that-a filteringcartridge having an upstream chamber 25 approximately 1.2 inchesdeep'and a downstream chamber 26 approximately 2.5 inches deep has beentested and that the test results have indicated that the non-wovenpacking requires replacement just about twice as often as the activatedcarbon medium. Specifically, it is believed that a practicalmaintanenceprocedure is to replace the packing 25a after approximately2,000 recordings have been made and to then replace thecompletecartridge after another 2,000 recordings have been made.

CONCLUSION In view of the foregoing, it will be now appreciated that arelatively economical and efiicient filtering system for suppressing thewaste products that are released during the operation of a drum-type,pyrographic recorder has been provided. The filtering system hasrelatively few moving parts and relatively long lived filtering elementsand is, therefore, fairly simple to maintain. Moreover, it not onlyremoves most, if not all, waste products that are released during therecording process despite the turbulent air flow around the drum, but italso aids in countering the centrifugal forces acting on the recordingmedium to assist in retaining the recording medium in contact with thedrum.

What is claimed is:

1. In combination with a pyrographic recorder having a stylus forforming an image on a recording medium carried by a rotatable drum, afiltering system for suppressing waste products released while saidimage is formed; said filtering system comprising a funnel havfor thewidelspr'ead inthe efficiencies of the various commercially availableblowers, ranging from 'rela- Y tively low cost, inefficient units toexpensive but effective models), is efficiently transferred to theaperture The downstream chamber 26 is initially filled to capacity withthe activated carbon medium and provision partial vacuumjis constantlymaintained during operation of said system in an area immediatelyadjacent said drum, thereby causing waste product laden air to be drawnthrough said funnelto pass through said filtering means whereby wasteproducts are removed therefrom.

2. The combination of claim 1 wherein said filtering means comprises afirst stage for removing solid-waste products and a second stage forneutralizing gaseous waste products. r I

3. The combination of claim 2'wherein said second stage is charged withan activated carbon medium and includes means for ensuring that any airpassing through said filtering means flows through said medium evenafter extended periods of inactivity of said filtering means. I i

'4. In combination with a facsimile unit having a stylus forelectroresistive printing on a recording medium carried by a rotatabledrum as the stylus travels axially of the drum, a filtering system forsuppressing waste products released while said printing is performed,said filtering system comprising a funnel having a face positioned inclose proximity to said drum for precluding.

any appreciable localized separation of said recording medium from saiddrum and a drum length aperture in said face, an air moving devicehaving an inlet side and a discharge side, and a filtering meansinterposed be- 7 .be drawn through said aperture and to pass throughsaid filtering means so that waste products are suppressed.

5. The combination of claim 4 wherein said drum has a predetermineddirection of rotation, said stylus is moveable axially of said drumalong a predetermined line of travel, and said aperture is slightly inadvance of said line of travel as measured in the direction of saidrotation.

6. The combination of claim 4 wherein said filtering means comprises afirst stage filled with a replacable porous packing material fortrapping solid components of said waste products and a second stagecharged with an activated carbon medium for neutralizing gaseouscomponents of said waste products.

7. The combination of claim 6 wherein said second stage includes bafflesfor preventing air from traveling therethrough without passing saidactivated carbon medium.

8. The combination of claim 6 wherein said drum has a predetermineddirection of rotation, said stylus is moveable axially of said drumalong a predetermined line of travel, and said aperture is slightly inadvance of said line of travel as measured in the direction of rota-

1. In combination with a pyrographic recorder having a stylus forforming an image on a recording medium carried by a rotatable drum, afiltering system for suppressing waste products released while saidimage is formed; said filtering system comprising a funnel having a faceadjacent said drum with a substantially drum-length aperture extendinglongitudinally of said drum, said funnel positioned to prevent anylocalized separation of said recording medium from said drum, an airmoving device having an inlet side and an outlet side, and a filteringmeans interposed between said funnel and the inlet side of said airmoving device so that a partial vacuum is constantly maintained duringoperation of said system in an area immediately adjacent said drum,thereby causing waste product laden air to be drawn through said funnelto pass through said filtering means whereby waste products are removedtherefrom.
 2. The combination of claim 1 wherein said filtering meanscomprises a first stage for removing solid waste products and a secondstage for neutralizing gaseous waste products.
 3. The combination ofclaim 2 wherein said second stage is charged with an activated carbonmedium and includes means for ensuring that any air passing through saidfiltering means flows through said medium even after extended periods ofinactivity of said filtering means.
 4. In combination with a facsimileunit having a stylus for electroresistive printing on a recording mediumcarried by a rotatable drum as the stylus travels axially of the drum, afiltering system for suppressing waste products released while saidprinting is performed, said filtering system comprising a funnel havinga face positioned in close proximity to said drum for precluding anyappreciable localized separation of said recording medium from said drumand a drum length aperture in said face, an air moving device having aninlet side and a discharge side, and a filtering means inteRposedbetween said funnel and the inlet side of said air moving device,whereby a partial vacuum is constantly maintained during operation ofsaid system in an area immediately adjacent said drum alongsubstantially the entire length thereof to cause waste produce laden airto be drawn through said aperture and to pass through said filteringmeans so that waste products are suppressed.
 5. The combination of claim4 wherein said drum has a predetermined direction of rotation, saidstylus is moveable axially of said drum along a predetermined line oftravel, and said aperture is slightly in advance of said line of travelas measured in the direction of said rotation.
 6. The combination ofclaim 4 wherein said filtering means comprises a first stage filled witha replacable porous packing material for trapping solid components ofsaid waste products and a second stage charged with an activated carbonmedium for neutralizing gaseous components of said waste products. 7.The combination of claim 6 wherein said second stage includes bafflesfor preventing air from traveling therethrough without passing saidactivated carbon medium.
 8. The combination of claim 6 wherein said drumhas a predetermined direction of rotation, said stylus is moveableaxially of said drum along a predetermined line of travel, and saidaperture is slightly in advance of said line of travel as measured inthe direction of rotation of said drum.